1. Field of the Invention
The present invention relates to a heating device and, more particularly, to a crystal growth device for growing crystals.
2. Description of the Related Art
The quality of a crystal rod depends upon several factors, such as a crystal growing process, purity of a crystal raw material, etc. In particular, in the design of a crystal growth device, a heating zone provided for the molten crystal raw material has a direct influence on the crystal growth interface, the nucleation at an initial stage of the crystal growth, the grain size during the crystal growth process, and the like that are in connection with the quality of the final product of the crystal rod. Therefore, the research and development of the crystal growth device is always a subject concerned by the industry.
Referring to FIG. 1, a conventional crystal growth device 1 comprises a crucible 11 for receiving a crystal raw material, a heating member 12 surrounding the crucible 11 and movable relative to the crucible 11 along a top-bottom direction of the crucible 11 for heating the crucible 11, a heat conducting member 13 surrounding the crucible 11, and a pedestal 14 on which the heat conducting member 13 and the crucible 11 are placed.
During the crystal growth, the heating member 12 starts heating to provide a crystal raw material 100 contained in the crucible 11 with a fixed temperature heating zone. After the crystal raw material 100 is molten, the heating member 12 is moved upwardly relative to the immobilized crucible 11 such that the molten crystal raw material 100 begins to proceed nucleation and crystal growth along with the varying temperature (i.e. the lowering of the temperature) of the heating zone resulting from the movement of the crucible 11 relative to the heating member 12 and from the conduction of heat by the heat conducting member and the pedestal 14. Finally, a crystal rod is obtained.
When the conventional crystal growth device 1 is used to produce, for example, a polysilicon crystal rod, according to the research, if, during the crystal growth process, the crystal growth interface 101 of the molten silicon crystal raw material is controlled to have a flat, or even slightly convex crystal surface, the heat stress may be reduced. In addition, controlling of the efficiency and mass of the nucleation at the initial stage of the crystal growth may enhance the formation of the twin boundary to facilitate the elimination of the lattice defects such as, dislocation and to obtain polysilicon crystal rod with an improved quality. However, in the conventional crystal growth device 1, since a single temperature heating zone is formed by means of the heating member 12, control of the temperature gradient of the heating zone is insufficient, and the key factors of crystal growth, such as nucleation, the form of the solid-liquid grain interface 101 and the like are difficult to handle effectively when the silicon crystal raw material is grown in the crucible 11.
In addition, when the crystal rod is prepared by such as the Bridgeman method, the crucible is lowered away from a heating unit that generally includes a top heater and an annular side heater that are mounted separately. A cooling water circulation device is additionally disposed in a base plate in order to enhance the control of the crystal growth speed. Although the initial crystallization speed in the bottom of the crucible may be increased, similar to the conventional crystal growth device 1, it is difficult to control the heating zone of the solid phase region and the solid-liquid interface. In addition, the molten crystal raw material in the crucible may begin to solidify at the surface thereof as the heaters are moved gradually away from the molten crystal raw material. Furthermore, the movement of the crucible is liable to cause the crucible to damage due to vibration, and interfere with the crystal growth.
In addition, to further improve the crystal growth quality, for example, Taiwanese Utility Model No. M386302 and Taiwanese Patent Publication No. 201111566m disclose a technique that provides a special heat conduction design for a base plate.
However, a polysilicon crystal rod with a better quality is still required for the rapidly increasing development of the semiconductor industry and photoelectric industry. Therefore, it would be desirable to provide a crystal growth device that has a more precise temperature gradient control for a heating zone.